The present invention relates generally to the technology of synchronizing cycle master and cycle slave nodes in one or more networks or sub-networks, and, more particularly, to a technique for synchronizing a cycle master node to a cycle slave node using synchronization information from an external network or sub-network which is supplied to the cycle slave node.
In conventional networks, various electronic components (e.g., computers, consumer electronics devices, appliances, office automation equipment, etc.) are interconnected by a local bus (typically a serial bus, such as the serial bus defined by the IEEE 1394 standard, which is commonly referred to as the "IEEE 1394" bus). Each of the components interconnected by the local bus are referred to as "nodes" on that bus. Typically, one of the nodes on the local bus (commonly referred to as the "local cycle master") serves to generate and distribute a common cycle clock to all other nodes (commonly referred to as "cycle slave nodes") on that bus. In general, each of the cycle slave nodes has a cycle timer which is synchronously updated by the local cycle master.
Some networks consist of a plurality of individual networks (each of which has its own local bus). These individual networks within the overall network are commonly referred to as "sub-networks". The sub-networks are linked or interconnected by one or more "bridges".
Some networks employ network-wide cycle clock ("cycle") synchronization. When the network is subdivided into sub-networks, the local cycle master of each sub-network must be synchronized to the network-wide ("global") cycle master in order to ensure the network-wide clock synchronization. In such networks, each of the local cycle masters are located in one or more of the bridges within the network. Typically, each local cycle master is contained within a "bridge portal".
For example, in a known network having two sub-networks which are interconnected by a bridge having a first bridge portal connected to the local bus of a first one of the two sub-networks, and a second bridge portal connected to the local bus of a second one of the two sub-networks, the local cycle master for the first sub-network is contained in the first bridge portal, and the local cycle master for the second sub-network is contained in the second bridge portal. Network-wide clock synchronization is achieved by passing the clock synchronization information between the local cycle masters (i.e., between the first and second bridge portals). However, it is not always desired or even possible to locate the local cycle masters in the bridges. Thus, what is required is a technology which allows a non-bridge node to be the local cycle master while ensuring the network-wide clock synchronization through one or more bridges within the network. More broadly, what is presently needed in this field is a mechanism to synchronize a cycle master node to one of the cycle slave nodes within a network which includes one or more sub-networks. The present invention fufills this need.